Causes

How sex organs form in the womb

A baby's genetic sex is established at conception, based on the sex chromosomes. The mother's egg contains an X chromosome, and the father's sperm contains either an X or a Y chromosome. A baby who inherits the X chromosome from the father is a genetic female (two X chromosomes). A baby who inherits the Y chromosome from the father is a genetic male (one X and one Y chromosome).

Male and female sex organs develop from the same tissue. Whether this tissue becomes male organs or female organs depends on the chromosomes and the presence or absence of male hormones.

In males, a region on the Y chromosome triggers the development of testicles, which produce male hormones. Male genitals develop in response to male hormones from the fetal testicles.

In a fetus without a Y chromosome — without the effects of male hormones — the genitals develop as female.

How ambiguous genitalia occurs

A disruption of the steps that determine sex can result in a mismatch between the appearance of the external genitals and the internal sex organs or the genetic sex (XX or XY).

A lack or deficiency of male hormones in a genetic male fetus can cause ambiguous genitalia, while exposure to male hormones during development results in ambiguous genitalia in a genetic female.

Mutations in certain genes can influence fetal sex development and cause ambiguous genitalia.

Chromosomal abnormalities, such as a missing sex chromosome or an extra one, also can cause ambiguous genitalia.

In some cases, the cause of ambiguous genitalia may not be determined.

Possible causes in genetic females

Prenatal exposure to male hormones. Certain drugs that contain male hormones or that stimulate production of the male hormones in a pregnant woman can cause developing female genitals to become more masculine. A developing baby also may be exposed to excess male hormones if the mother has a disease or condition that causes hormone imbalance.

Tumors. Rarely, a tumor in the mother can produce male hormones.

Possible causes in genetic males

Causes of ambiguous genitalia in a genetic male may include:

Impaired testicle development. This may be due to genetic abnormalities or unknown causes.

Androgen insensitivity syndrome. In this condition, developing genital tissues don't respond normally to male hormones made by the testes.

Abnormalities with testes or testosterone. Various abnormalities can interfere with the testes' activity. This may include structural problems with the testes, problems with production of the male hormone testosterone or problems with cellular receptors that respond to testosterone.

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